This invention relates generally to a semiconductor device and a method of manufacturing the same and, in particular, to a method of manufacturing semiconductor devices having a thin film formed on an insulating support, such as a substrate or support layer, and, further, to the formation of thin film transistors (TFTs) on insulating supports for large area image arrays, such as liquid crystal display panels.
Studies and experiments have been performed to form a high quality semiconductor films, devices, and IC structures on insulating supports, such as, insulating substrates, for example, glass, quartz, or the like and on amorphous layers, for example, SiO.sub.2, Si.sub.3 N.sub.4, and the like.
In recent years, expectations and desires for improved high quality semiconductor silicon devices and IC structures formed on these insulating supports has continually increased. Examples of applications are large area, high resolution liquid crystal display panels and devices; high speed, high resolution contact type image sensors; three dimensional ICs, and other IC structures. Therefore, the development of a method that will consistently and reliably form high quality silicon thin films on an insulating support is under intensive research and development. Relative to semiconductor materials, a polycrystalline or polysilicon silicon TFT device has a higher field effect mobility than an amorphous silicon TFT device and the amount of ON current of a polysilicon TFT is much greater than that of an amorphous TFT. However, the mobility of present polysilicon TFTs is still lower than that of monocrystalline TFT devices because of many barriers around the boundaries of crystal gains in the polysilicon material. In the case of the above mentioned applications, it is highly desirable to increase the level of mobility of polysilicon TFT devices to approach that of monocrystalline silicon. In order to obtain such higher levels of mobility in polysilicon TFT devices, the grain size diameter of the polysilicon should be increased from around 500 .ANG. to several 1,000 .ANG., which is in the range of reproducibility in the present state of the art, to about 1 .mu.m or greater.
Relative to the formation of thin film transistors (TFTs) on insulating structures, the following general methods have been studied and developed: (1) The formation of TFTs employing amorphous silicon as the semiconductor material fabricated by plasma CYD or low pressure chemical vapor deposition (LPCVD) or a similar process, (2) TFTs employing polycrystalline silicon as the semiconductor material fabricated by chemical vapor deposition (CVD), LPCVD, plasma enhanced chemical vapor deposition (PECVD) or similar process, and (3) TFTs employing single crystal or monocrystallized silicon as the semiconductor material fabricated by melting recrystallization or such similar process. However, the realization of high quality TFTs has been very difficult because the field effect mobility of TFTs comprising amorphous silicon or polycrystalline silicon is substantially lower than that of TFTs comprising single crystal silicon. For example, relative the conventional methods of (1) and (2), the field effect mobility for amorphous silicon TFTs is typically below 1 cm.sup.2 /V.multidot.sec and for conventional polycrystalline silicon TFT is approximately or less than 10 cm.sup.2 /V.multidot.sec. Thus, high speed operational characteristics have not been realized by the employment of these methods. On the other hand, in the case of the method (3), melting recrystallization, wherein a laser beam is utilized to bring about recrystallization, higher mobilities have been achieved, such as in the hundreds of cm.sup.2 /V.multidot.sec. However, there are problems associated with this technique due to the use of very high temperatures in processing and, furthermore, the technique has not been sufficiently developed to lend itself to mass production of semiconductor devices, particularly, the mass production of hundreds to thousands of active elements on a large area insulating supports, such as glass substrates for large area image devices, e.g., liquid crystal display panels.
Recently, the method of forming large grain polycrystalline silicon layers or films by solid phase recrystallization has been pursued and research employing this method has been proceeding in recent years. One of the principal reasons for the interest in solid phase recrystallization is the advantage in using lower processing temperatures compared to melting recrystallization. Examples of studies relating to solid phase recrystallization processing are found in the articles of P. Kwizera et al., "Annealing Behavior of Thin Polycrystalline Silicon Films Damaged by Silicon Ion Implantation in the Critical Amorphous Range", Thin Solid Films, Vol. 100(3), p. 227-233, (1983), and T. Noguchi et al., "Low Temperature Polysilicon Super-Thin-Film Transistor (LSFT), Japanese Journal of Applied Physics, Vol. 25(2), p. L121-L123, February, 1986 and in U.S. Pat. No. 4,693,759.
Generally, the conventional method of solid phase recrystallization relative to the formation of TFTs and other such active elements is that, first, a polycrystalline silicon film is formed by LPCVD or PECVD employing SiCI.sub.4, SiH.sub.4 or the like. Next, the polycrystalline silicon film is amorphized by a Si.sup.+ ion implantation. Then, the converted amorphous film is heat treated, for example, at approximately 600.degree. C. in an nitrogen atmosphere in excess of 30 hours and, preferably nearly 100 hours to produce large gain polysilicon. Finally, the polysilicon film is patterned into a TFT device using conventional photolithography techniques. However, the practice of this method has the following disadvantages: (1) The process is complicated by the requirement that the formed polycrystalline silicon layer must be amorphized before further treatment, which naturally increases manufacturing costs. (2) This amorphization is accomplished with expensive ion implantation system, which is necessary to perform the implantation operation. (3) The required heat treatment period is comparatively a very long period of time, in many cases as long as nearly 100 hours to achieve the largest grain size possible. (4) It is very difficult to handle large insulating substrates, such as, for example, 30 cm.times.30 cm, and obtain uniform results across a deposited and heat treated thin film on such a substrate. (5) The crystallized volume fraction, i.e., the crystal to overall volume rates in the recrystallized film, is low after performing solid phase recrystallization. Therefore, it is very difficult to fabricate a high quality active elements on large area substrates employing conventional methods of solid phase recrystallization.
It is an object of this invention to provide a low temperature method of forming polycrystalline thin films on an insulating support having high polycrystalline quality, larger crystal grains and good crystal grain orientation.
It is another object of the present invention to provide semiconductor devices, such as TFTs, having high speed operational characteristics and higher field effect mobility compared with such devices made by conventional methods.
It another object of this invention to provide a semiconductor device which comprises a polycrystalline silicon thin film formed on an insulating support characterized by large grains, high crystallized volume fraction and reduction of the Si/SiO.sub.2 interface state density.
It is another object of this invention to provide a method for the manufacture of a thin film polysilicon semiconductor that is simpler in implementation with resulting higher manufacturing reproducibility and yields compared to prior conventional methods.
It is still a further object of this invention to provide a polysilicon thin film on an insulating medium having high field effect mobility suitable for large are IC applications, such as large area TFT arrays for LCD panels.